The polyphenylene ether resins and acrylonitrile-butadiene-styrene or alpha-methyl styrene (ABS) resins are well known thermoplastic materials that are commercially available. Both of these materials are flammable and require the use of additives to achieve a commercially acceptable degree of flame retardancy.
If a thermoplastic test bar burns vigorously enough for a sufficient time, the bar will gradually soften (absent an unexpected crosslinking reaction) and will begin to exhibit sagging. As the bar becomes softer and less viscous, a point will be reached at which the bottom portion of the bar will separate physically from the remainder of the bar retained in the test stand. This phenomenon is known as "dripping".
In the prior art there have been problems in preparing flame retardant compositions of these materials which did not form flaming droplets when they are ignited with a direct flame.
U.S. Pat. No. 3,671,487 discloses a non-dripping linear polyester molding composition that employs a glass reinforcement, a flame retardant additive and a polytetrafluoroethylene resin. This reference employed about 0.5 to 2.5 parts by weight per hundred parts of composition of polytetrafluoroethylene.
Applicants have found that it is possible to achieve a flame retardant, non-dripping polyphenylene ether molding composition by the addition of a flame retardant compound and from 0.1 to 0.25 parts by weight per hundred parts of composition of polytetrafluoroethylene. In the case of ABS, a flame retardant compound and from 0.5 to 3 parts by weight per hundred parts of composition will be sufficient to produce a flame retardant non-dripping composition without a glass reinforcement. Accordingly, it is a primary object of the present invention to prepare flame retardant, non-dripping molding compositions of polyphenylene ether resins and ABS resins.
It is also an object of the present invention to provide flame retardant non-dripping molding compositions of polyphenylene ether resins and ABS resins that have physical properties which are not appreciably affected by the presence of the flame retardant-drip preventing system.